In order to improve the high efficiency and clean utilization of coal in graded conversion, an experimental system for coal pressurized pyrolysis was established. And taking the coal of Shaanxi Heilonggou as the object to study the effects of different temperatures(500 to 700 ℃), pressures(0.1 to 0.5 MPa), atmosphere(N2 and gas)and particle sizes(0 to 3 mm and 0 to 6 mm)on the yields and qualities of coal pyrolysis tar and gas at low temperature. The results show that with the increase of temperatures, the tar yield increases firstly and then decreases when reaching the highest at 600 ℃, the gas yield increases. With the increase of the pressure, the pyrolysis tar yield increases in the atmosphere gas and decreases in nitrogen atmosphere while the pyrolysis gas yield reduces in the gas atmosphere and increases in nitrogen atmosphere. The yield of pyrolysis tar is higher than that of small granular coal, but when the pressure reaches 0.5 MPa, the pyrolysis tar and the gas yield are almost unaffected by particle sizes. In the meantime, the increase in pressures reduces the amount of CO and H2 in the pyrolysis gas, but promotes the precipitation of more light hydrocarbons(such as CO2, CH4, C2H4, C2H6), increasing the calorific value of pyrolysis gas. Meanwhile, improving the quality of tar with the increase of the actual yield of benzene, toluene, phenol, and naphthalene in pyrolysis tar.